Field of the Invention
The present invention relates to a non-contact power transmitting and receiving system.
Description of the Background Art
A non-contact power transmitting and receiving system which supplies electric power to a load in a contactless manner is applied for charging a portable electronic apparatus, an electric vehicle and the like. In the non-contact power transmitting and receiving system, electric power is transmitted through a high-frequency power supply, a power transmission unit, a power reception unit, a rectification unit, and a load in the order presented.
In the non-contact power transmitting and receiving system, variable factors in transmission efficiency, such as variations in an equivalent resistance component of the load, variations in coupling coefficient due to misalignment when aligning the power transmission unit and the power reception unit, and variations in LC constant in the power transmission unit or the power reception unit, may occur. Some techniques have been proposed in which, even if these variable factors occur, the power factor of electric power supplied from the high-frequency power supply is maintained favorably to perform efficient power transfer.
Japanese Patent Laying-Open No. 2002-272134 discloses a technique in which, in a non-contact charging system, an inverter used for a high-frequency power supply has a variable frequency for improving transmission efficiency. Japanese Patent Laying-Open No. 2012-130173 discloses a technique for adjusting capacitor capacitance for improving transmission efficiency.
As shown in Japanese Patent Laying-Open No. 2002-272134, however, when the frequency of the inverter on the power transmitting side is changed, the inverter frequency disadvantageously deviates from set frequency (resonance frequency) of a resonant circuit or a filter circuit to degrade frequency characteristics of a power transmission path, resulting in reduced transmission efficiency. When providing an additional circuit for adjusting capacitor capacitance on a power transmission path as described in Japanese Patent Laying-Open No. 2012-130173, the system will be increased in size because of the addition of the circuit, resulting in increased installation space and increased cost.